High speed, which may be 1200 to 1800 rpm, natural gas engines in industrial applications such as gas compression and power generation producing 500 kW to several megawatts of shaft power are typically turbocharged and intercooled and often employ twelve or more cylinders arranged in a “V” configuration. This configuration results in a large volume of combustion gases in the intake system, especially on engines where the intake manifold is on the outboard side of the “V.” Gaseous fuel may be introduced into the air stream at the inlet of the compressor, resulting in a highly combustible air-fuel mixture throughout the entire intake system. This mixture has the potential to ignite in the intake system upon encountering an ignition source such as a combustion gas from an improperly seated intake valve. Once the air-fuel mixture ignites, the flame will travel extremely rapidly toward the charge air cooler, crossing over into the opposite intake manifold, thus igniting a substantial volume of fuel and leading to an intake manifold overpressure event, which may be called a backfire, that significantly exceeds typical operating pressures.
A variety of countermeasures have been employed in these engines to withstand potential overpressure, including building the intake manifold with sufficient thickness and material to withstand to accommodate potential overpressure. A flame arrestor may also be part of such engines to quench flames.
Other techniques have been used in an attempt to eliminate or reduce overpressure events. For example, the use of timed port injection of fuel, with a solenoid at the intake port of every cylinder a short distance upstream of the intake valves. Fuel injection takes place only when the exhaust valves are closed and the intake valves are open. This technique significantly reduces the volume of the air-fuel mixture in the intake manifold, which reduces the likelihood of intake manifold overpressure. While this configuration is often used on medium speed gas engines, this configuration adds significant cost and complexity and is seldom used on high-speed gas engines. Furthermore, such events can still occur, such as when an injector malfunction results in a continuous stream of fuel.
Another technique to reduce intake manifold overpressure is to reverse the location of the intake and exhaust manifolds, so that the intake manifold is inside the “V”-bank and the exhaust manifold is on the outboard side. This configuration significantly reduces the volume and length of the intake manifold, thus minimizing intake manifold overpressure intensity from combustion of the air-fuel mixture. While some engines are capable of using this configuration, other engine configurations do not permit reversing the location of the intake and exhaust manifolds without significant redesign of the engines, potentially compromising operational characteristics and leading to substantial cost burden.
An array of pressure relief valve or burst disks may also be located in strategic locations around the intake manifold. However, in addition to added cost, pressure relief valves may not reseal and burst disks need replacement after an intake manifold overpressure event. Such devices have also been inconsistent in actual operation with variations in actuating pressure, potentially still permitting excessive intake manifold overpressure events.
Some engines may incorporate a combination of such elements. Regardless of the countermeasures incorporated, the possibility of an intake manifold overpressure event is always present in natural gas engines, especially on engines where fuel is introduced significantly upstream of a cylinder's intake ports.
Thus, there is a need to reduce the severity of fuel ignition events should they occur and limiting the extent of such events.